Neutral chiral cyclopentadienyl Ru(ii)Cl catalysts enable enantioselective [2+2]-cycloadditions

Abstract

A chiral version of the Cp*Ru(COD)Cl complex equipped with an atropchiral cyclopentadienyl (Cpx) ligand enables [2+2]-cycloadditions between bicyclic olefins and alkynes with excellent reactivity and enantioselectivity. A streamlined synthesis of the Cpx ligand by a C–H functionalisation approach is shown. The chloride counterion of the neutral CpxRuII complex is essential for enantioselectivity.

Nickel‐Catalyzed Asymmetric [2+2] Cycloaddition Reaction of Hetero‐Bicyclic Alkenes with Internal Alkynes

“…By employing ruthenium catalyst, the group of Tam has further studied the scope of alkynes using a number of internal electron‐deficient alkynes . Most recently, the group of Cramer uncovered the asymmetric [2+2] cycloaddition reaction of oxabenzonorbornadienes with 1‐alkynyl triazenes and elaborated the product by a range of nucleophiles . To the best of our knowledge, the asymmetric [2+2] cycloaddition reaction of azabenzonorbornadienes with internal alkynes have not been reported.…”

“…On the basis of our own knowledge and references of the [2+2] cycloaddition reactions of bicyclic alkenes with terminal alkynes, we have proposed a mechanism as depicted in Scheme . The catalytic cycle would be initiated by the coordination of Ni(COD) 2 and ( R )‐SIPHOS‐Ph‐Mor to form the chiral nickel catalyst A , which coordinates with the alkyne 2 a to afford intermediate B .…”

Synthesis of (−)‐Hebelophyllene E: An Entry to Geminal Dimethyl‐Cyclobutanes by [2+2] Cycloaddition of Alkenes and Allenoates

“…Since previous methods to form geminal dimethylcyclobutanes in natural product synthesis [3,4] do not provide access to the key β-cyclobutylacetate motif, development of such a method was required to ensure a concise synthesis. We intended to form the unusual cis -fused cyclobutane core by enantioselective alkene–allenoate [2+2] cycloaddition [5–8] followed by diastereoselective reduction (Scheme 1a). …”

Synthesis of (−)‐Hebelophyllene E: An Entry to Geminal Dimethyl‐Cyclobutanes by [2+2] Cycloaddition of Alkenes and Allenoates

“…[1] Although this class of natural products has shown potential for nursery inoculation of conifer seedlings for better growth and survival in the fields,n os ynthetic access has been reported to date. Since previous methods to form geminal dimethylcyclobutanes in natural product synthesis [3,4] do not provide access to the key b-cyclobutylacetate motif,d evelopment of such am ethod was required to ensure ac oncise synthesis.W e intended to form the unusual cis-fused cyclobutane core by enantioselective alkene-allenoate [2+ +2] cycloaddition [5][6][7][8] followed by diastereoselective reduction (Scheme 1a). Since previous methods to form geminal dimethylcyclobutanes in natural product synthesis [3,4] do not provide access to the key b-cyclobutylacetate motif,d evelopment of such am ethod was required to ensure ac oncise synthesis.W e intended to form the unusual cis-fused cyclobutane core by enantioselective alkene-allenoate [2+ +2] cycloaddition [5][6][7][8] followed by diastereoselective reduction (Scheme 1a).…”